The present invention relates to a fuel cell system comprising a fuel cell using a hydrocarbon type fuel as a fuel and oxygen or air as an oxidant.
As the fuel of a fuel cell, there are used, for example, a hydrogen gas, or hydrocarbon type liquid or gaseous fuel. Fuel cells using a hydrocarbon type fuel include those of type reforming a fuel by a reforming apparatus to obtain a hydrogen gas and generating electricity using this hydrogen gas as a fuel, and those of type generating electricity using a directly supplied hydrocarbon type fuel. In the latter type cell, there is no necessity to use a reforming apparatus, and the size of a fuel cell system can be decreased.
Regarding the latter type cell, a reaction in a fuel cell using, as a hydrocarbon type fuel, for example, methanol is shown below.
Fuel electrode: CH3OH+H2Oxe2x86x92CO2+6H++6exe2x88x92
Oxidant electrode: 3/2O2+6H++6exe2x88x92xe2x86x923H2O
Total cell reaction: CH3OH+3/2O2xe2x86x92CO2+2H2O
As described above, carbon dioxide is produced as a product in a fuel electrode, in the fuel cell of type using a fuel directly. Therefore, a substance discharged from the fuel electrode contains a not-consumed fuel, carbon dioxide and the like. And, there was a problem that an increase in the amount of carbon dioxide by such powder generation raises the internal pressure of the fuel cell, thereby causing leakage of a fuel, decrease in cell performance and the like.
In contrast, there has been suggested, for example, a fuel cell system having a produced gas discharging mechanism which separates carbon dioxide and fuel from a substance discharged from a fuel electrode, by using a porous material constituted of a fluorocarbon resin, and selectively discharges only carbon dioxide out of a system (for example, Japanese Laid-Open Patent Publication No. 2001-102070, U.S. Pat. No. 4,562,123, and the like).
The above-mentioned produced gas discharging mechanism will be described referring to FIG. 5. FIG. 5 is a schematic cross-sectional view showing the structure of a fuel cell having a produced gas discharging mechanism. In the fuel cell shown in FIG. 5, a catalyst layer 54 and a gas diffusion layer 53 at the fuel electrode side and a catalyst layer 56 and a gas diffusion layer 57 at the oxidant electrode side sandwich an electrolyte membrane 55 to constitute an electrogenerating portion, and a fuel supplying tube 52 for supplying a fuel and a separation membrane 51 for selectively discharging carbon dioxide are provided. The separation membrane 51 is provided in contact with the fuel supplying tube 52, which is a passage for fuel leading to the gas diffusion layer 53, and carbon dioxide generated in the catalyst layer 54 is discharged out of the fuel cell via this separation membrane 51.
On the other hand, a user of a fuel cell has to exchange a fuel accommodating container when the remaining amount of a fuel decreases. Therefore, the user of a cell has to previously acknowledge a time of exchanging the fuel accommodating container. Regarding this matter, the remaining amount of a liquid fuel is made visible conventionally by installing a methanol consumption amount sensor using infrared ray, or by constituting a part of the fuel accommodating container with a transparent or semi-transparent material, for example.
However, the conventional produced gas discharging mechanism as described above cannot completely separate carbon dioxide and fuel selectively, and only can separate liquid and gas by utilizing a difference in surface tension onto a separation membrane. For this reason, not only carbon dioxide but also a fuel and other by-products than carbon dioxide produced in oxidizing the fuel are evaporated and discharged in the state of gas out of a fuel cell through the separation membrane.
A fuel and by-products thus discharged out of the fuel cell may contain a lot of substances having high toxicity and risk. For example, when methanol is used as a fuel, a fuel methanol and, formic acid, formaldehyde and the like that may be possibly produced as by-products in oxidizing the fuel, are deleterious substances, and evaporation and leakage out of a fuel cell of these compounds is a very important problem.
The present invention has been accomplished for solving the conventional problems as described above, and an object thereof is in a fuel cell system to completely prevent not only leakage of a fuel and by-products produced in oxidizing a fuel, but also leakage of them out of a fuel cell by evaporation. Simultaneously, another object of the present invention is to provide a fuel cell system capable of detecting the remaining amount of a fuel with high accuracy without separately providing a system detecting the remaining amount of a fuel.
For solving the above-mentioned problem, the present invention provides a fuel cell system comprising: an electrogenerating portion having a fuel electrode, an oxidant electrode and an electrolyte membrane disposed between the fuel electrode and the oxidant electrode; a fuel accommodating container accommodating a fuel to be supplied to the fuel electrode; and a fuel discharging portion connected to the fuel electrode, characterized in that the fuel accommodating container, the fuel electrode and the fuel discharging portion are air-tightly connected.
It is preferable that the fuel cell system further comprises a product absorbing portion for absorbing a fuel oxidized product discharged from the fuel electrode.
In this case, the fuel oxidized product may contain carbon dioxide.
Further, the fuel oxidized product may contain a compound having a carboxyl group.
Furthermore, the fuel oxidized product may contain a compound having an aldehyde group.
Still further, the fuel oxidized product may contain a compound having a ketone group.
In the above-mentioned fuel cell system, it is preferable that the product absorbing portion absorbs the fuel oxidized product by physical adsorption.
Further, it is preferable that the product absorbing portion absorbs the fuel oxidized product by chemical adsorption.
It is preferable that the fuel cell system further comprises a gas detecting means for detecting the amount of carbon dioxide absorbed by the product absorbing portion.
It is preferable that the product absorbing portion and/or the fuel accommodating container is of cartridge type exchangeable by installing to the fuel cell system or detaching from the fuel cell system. Therefore, it is also preferable that the product absorbing portion and the fuel accommodating container are integrated.
While the novel features of the invention are set forth particularly in the appended claims, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings.